[BOLT] Fix test. NFC (llvm#124851)

Keep output files different for multiple tool invocations. Otherwise, it
causes issues with our internal testing infra.

Author: maksfb

bolt/test/AArch64/pad-before-funcs.s

@@ -15,7 +15,7 @@
 # RUN: llvm-bolt %t.exe -o %t.bolt.4.4 --pad-funcs-before=_start:4 --pad-funcs=_start:4
 # RUN: llvm-bolt %t.exe -o %t.bolt.4.8 --pad-funcs-before=_start:4 --pad-funcs=_start:8
 
-# RUN: not llvm-bolt %t.exe -o %t.bolt.8 --pad-funcs-before=_start:1 2>&1 | FileCheck --check-prefix=CHECK-BAD-ALIGN %s
+# RUN: not llvm-bolt %t.exe -o %t.bolt.1 --pad-funcs-before=_start:1 2>&1 | FileCheck --check-prefix=CHECK-BAD-ALIGN %s
 
 # CHECK-BAD-ALIGN: user-requested 1 padding bytes before function _start(*2) is not a multiple of the minimum function alignment (4).